Transformer.



C. LL G. FORTESGUE.

TRANSFORME,

APPLICATION FLED AU 12 SHBETSS EET l.

VWTNESSESI if v. my)

C. LB G. FORTESUUE.

TRANSFORMER.

-APPLIGATION FILED AUG.2.1909.

ggggg atented Fb. 23, 119K).

12 SHEETSA'SHEBT ATTOR N EY C. LE G. FORTBSGUF.

TRANSFORMER.

APPLICATION FILED AUG. 2, 1909,

1,1295463. atented. Feb. 23,

l2 SHEBTS*SHEET MTNESSES: INVENTOR ATTORNEY Tatened Feb. 23, l.

12 SHEETS-SHEBT 4.

C. LE G. FORTESGUu TRANSPORMER.

PPLIATION FILED AUG. Z, 1909, MWA@ INVHW ATTORNEY E@ @E am@ C. LE G. F(RTESCUEA TRANSPORMBR.

APPLICATION FILED AUG. 2. 1909,

f QQQS .Patented F50. 23, 1915.

12 SHEETSSH"ET VVITNESSES: INVENTOR BY d /7 ATTORNEY C. LE G. FOBTESCUB.

Td A NSFORME APPLICATION FILED Am, 2,

ATTORNEY I) 0 H W TRANSFORMER. Y APPLICATION FILED AUG.2,1909. n lQ-r Patented feb. f2.3, i915.

l l2 SHEETS-SHEET 9.

VVITNESSES: INVENTOR D SY ATTGRNEY C. LE G. PORTESGU'E. TRANSPOBMER.

APPLICATION FILED AUG. 2, 1909 1,129,463. Patented M1123, 1915 12 SHBBTS-SHBET l0.

INVENTOR ATTORNEY C. LE G. FORTESGUE.

THANSPORMER. APPLICATION FILED AUG. 2, 190!y 1 TL, l 29,463, .hmmm FQ. m5.

12 SHEETSSHEET 11.

WITNESSES: INVENTOR humm-@ek M5611@ *M 2 LATTORNEY Ci LE G. PORTESCUE.

TRANSPORMER.

APPLICATION FILED AUG.

@muted Feb. 1915.

12 SHEETSw SHEET l2.

INVENTR WITNESSES 1 ATTORNEY f UNITED STATES PATENT OFFICE.

CHARLES LE G. FORTESCUE, OF PITTSBURGH, PENNSYLVANIA, ASSIGNOR TO WEST- INGHOU'SE ELECTRIC AND MANUFACTURING COMPANY, A. CORPORATION 0F PENNSYLVANIA.

TRANSFOBMER.

Specification of Letters Patent.

Patented Feb. 23, 1915.

Application led August 2, 1909. Serial No. 510,854.

T0 all whom t may concern:

Be it known that I, CHARLES LE G. FOR- rnscun, a subject of the King kof Great Britain, and a resident of Pittsburgh, in the county of Allegheny and State of Pennsylvania, have invented a new and useful Improvement in Transformers, of which the following is a specification.

My invention relates to electrical apparatus and it has special reference to the windings and insulation of transformers which are adapted for use with very highvoltage circuits.

The general object of my invention is to provide such a winding and such an insulating structure that the stress exerted by the voltage of the coils shall be properly distributed through the insulation with a view to reducing the space occupied by,and the manufacturing cost of, high-voltage transformers andapparatus of this class.

My invention is applicable to all types of transformers but it is particularly adapted for application to transformers of the core type.

The fact that the voltage which a given thickness of insulating material is capable of withstanding, is dependent, not only upon the character of the insulation, but also upon the form of the conductors or terminals which are separated by the insulation, is well known. For example, when two needle points are connected to the terminals of a high voltage circuit and are gradually brought nearer together in air or some other insulating medium, it has been observed that the distance between them when an arc is formed is materially greater than the distance between spherical terminals of relatively large radius under similar conditions.

' This phenomenon is due to the difference in the stress distribution in the insulating medium when the different forms of conducting terminals are used. lVith certain forms of terminals the stress is very much higher in those portions of the insul ting medium near one -or both of the terminals than inl intermediate portions which are more remote. Consequently, the insulating properties of the nearer portions are first diminished, forming a corona at the terminals, which causes an increased stress on the more remote or intermediate portions of the dielectric and results in a complete breakdown.

It is evident that when two conductors areJ subjected to a difference of potential, a minimum thickness of dielectric between them is required to resist any given difference-of potential when their form is such that the rate of change of potential through anissnaa the insulation is uniform or when the electrical potential at any point in the insulation Y1s proportional to its distance from the terminals. These conditions exist when the conductors are in the form of parallel plates of infinite size, and are approximated when two parallel plates which are large relative to the distance between them, or when concentric hollow cylinders, of large diameters .and of great length relative to the difference in their radii, are used. Under the aforesaid condition, which .may be designated as the condition of uniform stress in the dielectric, no corona is produced but breakdown occurs at all parts of the dielectric simultaneously.

It is. obviously impossible, in the practical construction of transformers and other electrical devices, to maintain the most desirable conditions by modifying the form of the current-Conducting duced means for e ecting this result independently of the form of the coils or other conductors. By introducing a plurality of plates or conducting cylinders between the current-conducting parts, such as the winding of the transformer, and the nearest low- 'potential conducting body, such as the core member of the transformer, the insulating medium is divided into a series of relatively thin sections in each of which the proper stress distribution is obtained. By making the areas of the conducting lates, which are close to the high potentlal-conductor, sufficiently large, the stress inthe layers of the insulation which space them apart may be materially relieved. Each succeeding conducting plate serves to so redistribute the stress that, by making the areas of the more remote conducting plates substantially equal to the areas of the adjacent plates, the

arts, but I have introproper potential points in the transformen Wlnding or some other body which is electrically charged and for which protection 1s desired. Some diiiiculties are overcome by .this means, but electric disturbances are liable to be introduced, by reason of the fact that vthe"'conducting plates form a series of condensers, which, vunder. certainconditions, rupture the insulation lmmedlately surrounding the charged conductor.

' According to my 'present invention, I so ldispose the coils of the transformer winding and soconnect them to'y the Aconductors in the insulating medium as tof thoroughly and eiectively insulate allof the parts, the arrangement being such', in some cases, as to produce a' substantially uniform distribu-v tion of potential within the insulating-medium, and in otherpca'ses', to produce a distribution similar that .Which /would exist if the opposingsurfaces that are "insulated from' each 'other were extended infinitely, or

as 'far as possible. The coils are 'spaced lfrom theh core member and from the tank or ,casing in-accordance. with their dier- ,ences oitpotential therefrom, and the insulation' and the conductors therein are so shaped, disposed and connectedwith reference to the coils that all of said parts cooperate to p rotectl each other without unduly encumberingfthev transformer.

It will, Aof course, be understood that, wherever conducting cylinders or rings are herein referred to as surrounding the core legs da transformer, interrupted 'cylindersV orinterijupted ringsare meant: otherwise, the alternating inX in the core would obviously set upga short-circuited current in these parts. s

vMy invention is illustrated in the accomvpaiiyinfg drawings, in which- Fi res 1.and`2 are, respectively, a sectiona plan. view and a side "elevation of a transformer constructed in accordance therewith. Fi 3 is a partially sectional view of the trans ormer core and windings shown in Fig. 2. Fig. 4 isaview corresponding .a Fig. 3 'm which insulating and Conductc linders are disposed on all. of the ,trans ormercore legs. Fig. 5 is a view of a thm-Psse transformer core and windings .cerresponding to Fig-.3., and Fi 6 is a new, `coifi-eapondin ornnarhavi-ng` a ing, one section `being adjacent to the trans- Vformer core and the other section being outside the primary winding. Fig. 7 shows a miiiedsystem of connections or the highpqtential-coils of a transformer which is to Fig. 3, o a trans-v ivided secondary wind' adapted for testing purposes when it is'desired to ground one end of the winding and may also be used for groups of transformers which are star-connected, with their neutral point grounded on a three-phase circuit. Fig. 8 is a view of a'transformer in which the winding is divided into four groups and is distributed on the four legs of a substantially square or rectangular core instead ofron two legs, as is more usual. Fig. 9 illustrates an arrangement of transformer windings which is similar to F ig. 3 jexcept that the insulating barriers between the two groups of high-potential windings are omitted. Fig. 10 is a view of a winding corresponding to Fig. 3, in which rings of conducting material are either embedded in the insulation or are located between insulating cylinders and are connectedto inter- .mediate points in the transformer winding,

in place of the complete conducting cylinders of Fig. 3. Fig. 11 is a view of a transresistances. `Fig. 12 is a perspective view,

of an insulating sleeve having conducting cylinders which are connected` to vintermediatepoints in'the winding, as in Fig. 13, but are specially constructed to introduce resistance into the condenser or capacity circuit without the use of external resistances. Fig. 13 is a front elevation of a shell type transformer Aembodying my invention, certain of the parts being broken away tp disclose the coils. Fig. 14 is a plan viewof the core and windings shown in Fig. 13 and ...Fig 15 is a diagrammatic view showing the 4circuit connections for the windingof Figs.

13 and 14.

Refering to Figs. 1, 2 and 3 of the drawings, t e structure here illustrated com- -prises a substantially rectangular core 1, a low-potential windin 2 that is `divided into `two oups of coils which surround two :opposlte legs 3 and 4 of the core 1 and are separated therefrom by insulating sleeves 5, a primary windin composed of two groups 6 and 7 of relativel iat coils, insulating sleeves 8 and 9 locate on the respective core legs, between the lowV and high-potential windings, and insulating barriers 10 and 11 that separate the high-potential. windings from .each other vand from the walls of` a tank or casing 12 in 'which `the transformer is disposed.v The crelegs 3 and 4 may be. of any suitable form but are preferably cruciform in cross-section in order to economize space and to reduce the mean length of turn in the winding. The insulating sleeves 8' and 9 are similar to eachother and each preferably com rises a plurality of cylinders 13 of conducting inaist terial and insulating cylinders 14 which al` ternate therewith. rlhe conducting cylinf ders are of graded lengths,the longer ones being adjacent to the low-potential winding and the shorter ones adjacent to the high-potential winding. By this means, the surface distances between the conducting cylinders are made adequate to correspond to or to exceed the potential which the insulating cylinders are capable of withstanding.

It has been my aim to so arrange and connect the coils of the highgpotential winding as to obtain a maximum separation between the high-potential coils and the core, the coils of lower-potential being disposed at shorter distances from the core member in order to utilize the space within the core member to a maximum degree. If the lowest-voltage coils' of the high-potential winding are grounded, they may be located very close to the core structure, as shown in Fig; 2, but, if the potential difference between these coils and the core is liable to be great, they should be considerably .removed from the core member. The circuit connections for the 4primary windings are clearly set forth in Figs. 2 and 3,'to which special reference may now be had. As here shown, a connection may be completed from a highpotential external circuit through a conducting lead 15, which extends through a terminal bushing 16l and is connected at its inner end to a high-potential coil 17 of the winding. From this coil, a circuit is continued through the conducting cylinder 13 of largest diameter of the sleeve 8 to the inner' turn of a coil 18. From the outer turn of `this coil, a circuit is continued through the conducting cylinder 10a of smallest diameter of the barrier 10 to the outer end of coil 19. Circuit is similarly continued through coils 20, 21, 22, 23, 24, 25, 26, 27 and 28, the free terminal of coil 28 being grounded or connected to the outer turn of a coil 29 of the group 7. The cir- A cuit is completed through the coils of this group in the same way as it was completed through the coils of group 6, but in the reverse order, the leadv 30 being finally brought out through a terminal bushing 31. By interconnecting the coils through the conducting cylinders,`which are a part of the insulating sleeves, the strains imposed upon the insulation are distributed with substantial uniformity, irmspective of the areas of the conducting cylinders or the thickness of the insulating cylinders which separate them. The space occupied by the transformer may be materially reduced for a predetermined voltage, since each insulating cylinder may be called upon to resist a maximum potential without any tendency for adjacent insulating cylinders to be ruptured.

When the insulation is formed of a plu rality of alternating concentric cylinders of insulating and conducting materials, condensers are obviously formed which may produce potential disturbances in the transformer winding, when the connections are eiiected as shown in Figs. 2 and 3, but these disturbances are slight, if not altogether absent, in transformers which are supplied with alternating current at ordinary commercial frequencies and if the wave form of the alternating current supplied to the windings is free from high harmonics. In any event, the disturbances may obviously be avoided by utilizing certain modified constructions which are hereinafter described. It is my intention Ato include the use of insulation of the so-called condenser type within the scope of my invention without limiting myself in this regard.

When a transformer is designed for. very high voltage service, it may be found advantageous to provide insulating sleeves 32 and 33 on the transformer legs 34 and 35 as shown in Fig. 4 in order to increase the area of the-conducting cylinders which are located adjacent to the core member, without enlarging the dimensions of the core member itself. The advantage secured in this manner depends upon the principle which renders condensers of equal capacity desirable for insulation of this type, the increased areas of the small conducting cylindrical members making possible a reduction in length for a given diameter. These sleeves are composed of conducting cylinders 32a and 33a which are electrically connected by conductors 321 and 33b to the corresponding cylinders 34 and 35a of the other legs and are separated by suitable insulation 32c and 33C. Thus the conducting cylinders fern/ing a part of the insulating structure lon th four legs of the core mem* ber and nearest to them are interconnected, the next arger cylinders are similarly interconnected but independently of the others, etc., as clearly shown in Fig. 4.

rlhe transforma.q illustrated in Fig. 5 comprises a core 36 having three parallel legs \37, 38 and 39, and low and high-potential windings disposed on each leg to constitute a three-phase transformer, each phase corresponding to one half of the winding shown in Fig. 3. This arrangement is well adapted for three-phase star-connected transformers having their neutral points grounded. The same arrangement of coils may be adapted for star-connected transformers, in which the neutral point is not grounded, by providing sufficient insulation between the high-potential coils and the core to withstand the voltage between one of the high-potential line conductors and the neutral point.

The structure shown in F ig. 4 may, of course, be adapted for use with high-potential polyphase transformers, and the lowoutside of the groups of high-potential windings, as well as inside of said groups.

' The advantages obtained from this arrangenient are well known. When both ends of each of the transformer winding groups 6 and 7 are maintained at a relatively highpotential above the ground, the terminals 6a and 7a which are' interconnected are carried away from the core member through bushings 6b and 7b as shown in ig. 6, in order to avoid grounding.

Reference may now be had to Fig. 7 in which the two groups of high voltage windings are disposed substantially as they are in Fig. 3 'of the drawings, but are so connected that one terminal is adapted to be maintained at a relatively low potential while the other is adapted for a very high potential. If a terminal 40 is assumed to be connected to a higlrpotential conductor, the coil 41 to which it is connected is connected, at its inner end, to a coil 42, the circuit being continued, through coils 43 and 44, to coil 45. The opposite end of coil 4-5 is connected, through one of the conducting cylinders of the insulating sleeve 9, to coil 4:6 which is connected direct to the coil 47, a circuit being continued in a similar manner from the coil of one group to a second coil of the same group, through a conducting cylinder, from thence directly to a coil of the other group, circuit again being continued through a conducting cylinder.y The coils are successively connected, in the order of their reference numerals, from- 41 to 60, inclusive. This arrangement is specially adapted vfor use in transformers having one terminal grounded or in transformers which are star-connectedin groups of three', with their neutral point grounded. This arrangement may also be usedfor star-connected three-phase groups when the neutral is not grounded, provided 'Y v the lowfpotential coil of the higlrpotential winding is properly insulated for the differencein potential between one circuit of the three-phase s vstem and its neutral point.

Reference may now be had to Fig. 8, where the winding arrangement, in securing the desired distribution of potential, is such that the total amount of necessary insulating material is reduced to a very small quantity for high voltages, the space usually occupied by transformer coils.

t e insulation being occupied by additional AV substantially square core member 61, having similar groups of low-potential and high-potential coils disposed on each of the four legs of the core is ro-vided. One terminal of the transformer 'or the high-potential is connected to a coil insegue tween the groups of Fig. 3, the arrangement and connections of the coils being such as to permit of this modification. From acoil 82, a circuit is established through coils 83 to 109, inclusive, as indicated inFig. 9.

In Fig. 10, the arrangement of transformer coils is shown which is similar to that of Fig. 3, but, instead of the connections between coils being completed through the conducting cylinders which form a part of the insulating structure, a plurality of conducting rings 115, which may be embedded in an insulating bushing 116, are used. The rings are joined by conducting strips 115a which form the circuit connections between coils and, consequently, the potential of each pair of rings is fixed, their location relative to the core member being determined by their potential. The rings are so connected to the transformer winding that the potential of each is fiXed at a value which corresponds to the potential of the same surface in a field which would eXist between the high potential ring and the core member if their -parts were concentric conducting cylinders of infinite length. In other words, such a distribution of potential is established over the surfaces of the insulating body that eX- tend between the parts to be insulatedas will produce substantially the same static held or stress distribution as would exist if the said parts were cylinders of infinite length or other surfaces of infinite area. In the case of cylinders of ininite length,

the field or stress distribution between them With such an arrangement of parts, no conductor in the insulating structure has a definite capacity to any other conductor, but its capacity is a function of its own potential and those of the remaining conductors. Consequently, its potential, as determined by its connection to the transformer winding, canvnot be changed by resonance with the inductance of any portieri of the winding of the transformer, because such a change would at once cause a'change in capacity, which would immediately destroy the requisite condition for resonance. The conductnot overlap but their edges preferably come directly opposite each other, in order to obtain-the desired stress distribution in the insulation. lt is evident that insulating structures similar to the bushing 116 may be adapted to other winding arrangements and to polyphase transformers such as those illustrated in other figures. It is evident that the conducting rings described above may be utilized in connection with any well known winding arrangement and that this type ofl insulation may be combined with other types and structures of insulation within the scope of my invention. For instance,

in the transformer shown in Figs. 2 and 3, or vin .other figures, the spaced conductors forming a part of the insulating structure may be connected to such points of the winding as to produce substantially the same field distribution (logarithmic) as would exist if the outer cylinders were of infinite length. It is immaterial, so far as the attainment of this result is concerned, whether the conductors embodied in the insulation are cylinders extending throughout the length of the structure or rings at its ends only, so long as the said conductors determine the potentials upon the surfaces or boundaries of the insulating region in accordance with the loga rithmic law.

Referring to Fig. 11, the structure here shown comprises a plurality of insulating sleeves or bushings which are similar to those of Fig. 9 except that additional barriers 117 and 118 areintroducedbetween the two groups of transformer coils and between the groups in the. tank. These barriers permit of a more compact arrangement. The conducting cylinders, of which the insulating sleeves are composed, are severally connected to intermediate points in the transformer windings through resistance sections 119. The connections between coils are completed through conducting strips 120, which are either embedded in insulating sleeves 121, as shown, or may be disposed between concentric insulating cylinders. By connecting the intermediate points in the winding to the conducting cylinders of the insulating sleeves through resistances, the thickness of the sleeves may be materially reduced, since an advantageous distribution of potential through the insulation is maintained without danger of injuring the insulation immediately surrounding the coils, voltage disturbances producedin the plates of the condenser bei-ng choked out by the resistances.

In Fig. 12, the conducting cylinders of the insulating sleeves are provided with slots 150 which are cut alternately from opposite ends in order to form a zigzag path for the capacity current, thereby introducing a re'- sistance which is non-inductive and which tends'to prevent static disturbances in the same Way that the external resistances 119 of Fig. 11 accomplish this result.

The insulating sleeves and bushings referred to hereinbefore are preferably constructed as set forth in Patent No. 858,385,

granted July 2, 1907, to the Westinghouse Electric & Mfg. Co., as assignee of Emil Haefely, sheets of tin-foil, or other suitable conducting material, being interposed at convenient or desired intervals between the convolutions of insulating material, during the construction of the device.

Referring to Figs. 13, 14 and 15 of the drawings, a shell type transformer is here illustrated, comprising a core member 110, low-voltage coils 111 and high-voltage coils 112. The high-voltage coils are interposed between the low-voltage coils and are relatively narrow, being at the same time centrally located, relative to the adjacent walls of the core member, so that all the coils of the transformer have the same length of mean turn and are all concentric, while the high-voltage coils are separated from the core member in all directions and the lowvoltage coils are adjacent to the core member, the circuit connections which I prefer being shown in Fig. 15.

The distribution of the static field within the insulating structure is determined, as before explained, in accordance with the potentials of the conductors that are embodied therein, which potentials are fixed by the connections of the conductorsto the coils. The distribution of the static ield external to the insulating structure, however, is determined by the voltages and spacings of the coils which are adjacent thereto. ln other words, the potential of each coil determines the potential of a plane passing throughit substantially normal to the core leg that is surrounded by it. Since the connections of the coils to the conductors constituting a part of the insulating structure determine the potentials of the corresponding cylindrical surfaces that surround the core and include the said conductors, and, since the said conductors respectively terminate opposite to the coils to which they are connected, it will be seen that the ends of the insulating structure, or the ends ofthe region bounded by the said conductors, are shaped to substantially conform to the locus of the intersections of the substantially equipotential surfaces adjacent to the ends of the said structure.

Although most ofthe drawings illustrate windings applied to core typetransformers, those skilled 4in the art will understand that they are equally applicable to shell type transformers, and I desire that modifications which do not depart from the spirit llt of my invention shall be included Within its scope.

I claim as my invention:

1. The combination with a low potential body, and a relatively high potential winding comprising a plurality of coils, of an insulating structure interposed between said body and said winding and comprising al tornate layers of insulating and conducting materials, the layers of conducting material being superposed and constituting parts of the connections between the coils of the winding.

Q. The combination with a winding comprising aplllrality of coils, of an adjacent insulating structure comprising alternate layers of insulating and conducting materials, the layers of conducting material being superposed and constitutin parts of the connections between the coils o the winding.

3. The combination with a low potential body, and a relatively high potential winding comprising a plurality of coils, of an insulating member interposed between said body and said winding, and conductors adjacent to those surfaces of said'member that extend between the said body and said winding constituting parts of the connections be? tween the coils of the winding.

4. rlhe combination with a magnetizable core and a winding comprising a plurality of coils, of an insulating sleeve separating the coils from the core and having a plurality of concentric conducting cylinders embedded in it, said conducting cylinders constituting .portions of the electrical connections between the coils.

5. A transformer comprising a` substan- .tiallyrectangular core and a pluralityof coils disposed end to end, in two groups, on opposite legs of the core, and insulating sleeves disposed between the coils and the core legs onvwhich they are mounted, the coils being connected in a series of which 'the middle coils of the groups constitute the terminals.

6. A transformer comprising a core, a plurality of coils disposed thereon end to end, and an insulating sleeve separating the coils from the core, the connections between coils being completed through conductors embedded in the insulating sleeve.

7. A transformer comprising a core, an

insulating sleeve surrounding aportion of end to end to form a group, and an insulatwith a ma ing sleeve.separatingv the coils from the core,

y said sleeve comprising a seriesof concentric sulating sleeves separating the coil groups from each YotlieiggeaclLof said sleeves comprising alternate layersifconducting and insulating materials and said coils being interconnected through the agency of the conducting layers.

l0. A transformer comprising a substantially rectangular core, a plurality of coils disposed end to end in two groups on the respective opposite legs of the core, insulating sleeves separating the coil groups from the core legs and insulating sleeves separating the coil groups from each other, each of said sleeves comprising alternate layers of conducting and insulating materials and the said coils being connected through the agency of the conducting layersto form a series having its terminals at the innermost coils of the respective groups.

11. A transformer comprising a core having a plurality 'of substantially. parallel legs, low-voltage' coils disposed thereon, insulating sleeves surrounding the low-voltage coils and groups of high-voltage coils surrounding the insulating sleeves, the coils of each group being arranged end to end and connected in series from the innermost to the outermost, and the outer coils of each group being' connected together.

12. In a transformer, the combination etizable core and a winding therefor, o insulating means disposed 'between said core and said winding, and means constituting a part of the winding for rendering the distribution fof stress inthe insulation independent of the core'member.

13. In electric a paratus, the combination ywith a magnetiza'le-oore and a winding therefor and an insulating structure disposed between saidvcorehand said winding, of vineens forfe'ecting ay distribution of stress inthe insulation .which corresponds to that existing in a uniformrinsulating me dium between'vv two concentric conducting cylinders' of infinite' lengthA spaced at, the same distance apart and having di'erence of potential as thewinding and the core member.

145.111 atransformer, the combination withila subdantially .r i.; areore, two

'the' same l nuance groups of coils disposedon the respective opposite legs of the coreand an insulating structure comprising concentric cylinders of conducting materia 15. In a transformer, the combination with a substantially rectangular core, two groups of coils disposed on one pair of opposite legs, and insulating sleeves or bushings comprising alternating concentric. cylinders of insulating and conducting mates, rials separating the coils from the core legs,

of insulating sleeves disposed on the remaining pair of oppositecorelegs having alternating concentriccylinders of insulating and conducting materials, the conducting cylinders of the sleeves on core legs not occupied bythe coils being electrically connected to the conducting cylinders Aseparating the winding from the core legs to increase the effective' area' of the latter cylinders.

16. In a transformer, the combination with a substantially rectangular core and a plurality of coils disposed end to end on one pair of opposite corelegs in two similar groups, of insulating sleeves comprising a plurality of alternating cylinders of insulating and conducting materials surrounding the groups and separating them from each other, and sleeves or bushings comprising concentric cylinders of insulating and conducting materials, said coil groups being electrically connected by a conductor thread-,-

ed through the, insulating bushings or sleeves.. A

17. The combination with two conducting members, of-an interposed insulating structure, and'means for establishing a distribution of potential'adjacent to the surfaces of.

- the insulating structure thatextend between said members to produce a distribution of I,the static 'field in the insulating structure i faces of lthe conducting members were ex-` that substantially corresponds to the distri# bution that would exist if the vopposing surtended as far as possible or infinitely.

18; The combination with two conducting members, of an interposed insulating structure, conductors terminating adj acont to the ortions of the surface thereof that extend tween said members, and means for fixing the potentials of said conductors to produce a distribution of the static field in the insu lating structure that substantially corresponds to the distribution that would exist if the opposing surfaces of the conducting members were extended as far as possible or infinitely.

19. The combination with twosubstantiallyV cylindrical conducting members, of an Y interposed insulating structure and means for establishing a distribution of potential adjacent to the surfaces of the insulating structure that extend between said members to produce a distribution of the static field inthe insulating structure that substantially corresponds to the distribution that would exist if the opposing surfaces of the conduotinIg members were extended as far as possib e Aor infinitely.

'20. The' combination with Ytwo substantically'cylindrica'l conducting members, of an interposed insulating structure, conductors terminating adjacent to the portions of the surface thereof that extend between said members, and means for fixing the potentials of said conductors to produce a distribution of thel static field in the insulating ystructure 4that substantially corresponds to the distribution that would exist if the conducting members were of infinite length.

21. The combination with two conducting members, of interposed insulating material, and conductors interspersed with -the insulating material the potentials of which are severally fixed at substantially the same `values as would exist at the same points if the opposing surfaces of said conducting members were extended in similar form as far as possible orinfinitely.

22. The combination with two conducting members. lof an interposed insulating struc# ture, and conductors termina-ting adjacent to the portions of the surface thereof that extend between said members, the potentials of said conductors being severally fixed at substantiallyv the same Values as would exist at the same points ifthe opposing surfaces of the conducting 'members were extended in similar form as far as possible or inlinitely.

23. The method of insulating two conducting members from each `other which consists in fixing the potentials linijacent to the surface of an insulating. structure that .is interposed between .the members at sub#- sta'ntially the same Avalues as would exist at the-sameV points if the opposing surfaces of similar formas far as possible or infinitely.

24:. The method of insulating two conducting members from each other which lthat is tapered in opposite directionsfrom an intermediate point, and conductors that the conducting members were extended in terminate adjacent to the tapered faces of the structure and are connected to and included in circuit With the Winding.

26. An electrical device comprising a plurality of series-connected coils, an adjacent insulating structure that is tapered in opposite directions from an intermediate point, and conductors that terminate adjacent to the tapered faces of the structure and constitute parts of the connections between the coils.

27. An electrical device comprisingY a plurality of sidebyside series-connected coils, the coils of higher potential being disposed intermediate those of lower potential, an adjacent insulating structure that is tapered in opposite directions from an intermediate point, and conductors that terminate adjacent to the tapered faces of the insulating structure and are connected to the coils.

28. An electrical device comprising an insulating structure that is tapered from an intermediate point toward its ends, a plurality of side-by-side series connected coils, the coils of higher potential beingdisposed adjacent to the intermediate portion of the insulating structure and also intermediate the coils of lower potential, and conductorsV that terminate adjacent to the tapered faces of the insulating structure and are connected to the coils.

29. A transformer comprising a plurality of side-by-side coils thatare connected in a series beginning With intermediately located coils and ending With outer coils, an adjacent insulating structure that is tapered from an intermediate point toward its ends, and conductors that terminate adjacent to the tapered faces of the insulating structure and are connected to the coils. A

30. An electrical device comprising a winding, an adjacent insulating structure having its ends similarly stepped, and conductors that terminate adjacent to the steps in the insulating structure and are respectively connected to intermediate points in the Winding.

31. An insulating structure having similarly stepped ends and spaced conductors that terminate adjacent to the steps.

32. In an electrical device, the combination with a plurality of side-by-side coils, of insulating structures respectively Within and without the coils each comprising spaced conductors, and connections between the coils'including the said conductors.

In an electrical device, the combination `with a plurality of side-byside coils that are connected in a. series beginning with the centrally located coils and successively including the next outermost coils, of 'msulating structures respectively Within and .ithout the coils each comprising spaced conductors, the connections between the coils alternately including conductors of the respective insulating structures..

34. In an electrical device, the combination with a plurality of side-by-side series connected coils, of insulating structures respectively within and Without the coils each comprising spaced conductors, the connections between the coils alternately including conductors of the respective insulating structures.

35.v An insulating structureY comprising inner and outer conducting sleeves, an inter-y winding, a member surrounded thereby, an

insulating structure interposed between the Winding and said member, and spaced conductors in the insulating structure that constitute parts of the said Winding.

38. In an electrical device, the combination with a core comprising a coil-receiving portion and other portions extending transversely thereto, of a plurality of connected coils surrounding the said coil-receiving portion of the core, the coils of higher potential relatively to the core being more remote from the transversely extending portions o'f the core than the coils of lower potential.

39. In an electrical device, the combination with a plurality of side-by-side coils, of an insulating structure adjacent to the coils, and conductors that terminate adjacent to the ends of the insulating structure and are connected to the coils, the conductors being respectively opposite to the coils to Which they are connected.

40. In an electrical device, the combination with a plurality of side-by-side coils, of

an insulating structure adjacent to the coils, and conductors that terminateadjacent to the ends of the .insulating structure and are i connected to andincluded in circuit with the coils, the conductors being respectively opposite to the coils to which they are connected. i

41. An insulating structure of'gradually and similarly diminishing thickness from an intermediate point toward its ends, of spaced conductors that terminate adjacent to the tapered faces of the structure.

42; The combination with a plurality of side-by-side spaced coils, of an adjacent in-A sulating structure of gradually diminishing 

